Louis Althusser was a French philosopher who developed Marxist theories of ideology and how it shapes people's identities and sense of self. He argued that ideologies circulated by institutions like media and education covertly construct people's identities by categorizing them, without them realizing it. This causes people to lose their individuality and take on identities defined by gender, class, ethnicity and other stereotypes promoted by society's "ideological state apparatuses." Althusser used the concept of "interpellation" or "hailing" to describe how ideology shapes people into subjects that identify with certain groups and adhere to their rules and norms.